Turbo equipment typically includes a rotating shaft with impellers or blades that are borne by a radial bearing at either end of the rotating shaft. A thrust bearing is employed at one end of the shaft in order to accommodate axial loading of the rotating shaft assembly.
Typically dry gas or mechanical seals are used ensure that bearing oil lubrication is not mixed with process fluid and to contain high pressure gases from escaping. Dry gas seals use hydrodynamic air bearing affects to create small, non-contact gaps. These non-contact gaps are effective as sealants only when the surface speed between the sealing surfaces is relatively high and the bearing surfaces remain flat and pressed against each other to prevent seizure at speed and/or “Hang-ups.” Mechanical seals suffer from similar issues.
In contact based seals, areas of the shaft and seal are subject to wear and leakage and create a lot of noise e.g., lip seals. Brush and ablatable seals are a form of contact based seals that use centrifugal force or pressure differentials to keep them in contact with a respective mating surface. General wear on brush and ablatable seals create particulates that add significantly to maintenance costs; at high speeds, heat and frictional losses between the seals and shaft are significant. Labyrinth seals provide a form of non-contact seal that minimizes wear on the shaft caused by contact, but these non-contact seals provide a conductance path that can result in huge flows when there are pressure differentials across the seal. Leakages in non-contact seals are reduced by minimizing and elongating clearances in an axial direction between the rotating and stationary sections of the seal. This adds significant costs and is not always effective. In process equipment, bearing isolators are used to combine labyrinth and lip seal technologies. These isolators inject fluid or gas at a higher pressure than the flow pressure of the volume to be sealed, as seen in U.S. Pat. No. 7,631,878 (Orlowski).
In Turbo equipment, hydrodynamic oil bearings, such as spiral groove and foil bearing, are typically configured as either a sleeve or tilting pad to accommodate rotary loads or a tilting pad-type bearing to accommodate thrust loads. The bearings may be mounted in various configurations, such as, for example: stud mounting, where a rounded or spherical surface mates with a backside of a bearing pad, See, New Way Air Bearings' web site under “mounting components”; flexure mounting, where a bearing pad moves freely in various directions as a result of being mounted upon a compliant member e.g., a flexure or groove, See generally, U.S. Pat. No. 5,743,654 (Ide); elastomeric mounting, where a bearing pad has compliance from contact with an elastomeric member e.g., an O-ring type mount, See generally, U.S. Pat. No. 3,360,309 (Voorhis); a spring-type mounting that provides compliance to the bearing pad, e.g., Belleville washers; and any other suitable mount, such as, linkages, hardened balls, rods, pins, etc.
The hydrodynamic oil bearings provide non-contact seals, such as gas and labyrinth seals, based on the viscous dragging of a fluid or gas into a small gap. The oil bearings build up a pressure “wedge” as certain speeds are reached. See generally, Pall Corporation and Carbone Turbograph gas seals; U.S. Publication No. 2006/0062499 A1 (carbon graphite, ceramic materials, pressurized gas in high-speed turbine engines). Typically small electric motor compressors e.g., oil-free positive displacement compressors, pneumatically-driven positive displacement compressors, or multi-stage centrifugal compressors, that are direct driven, high speed, and constructed with stainless steel and without internal seals or oil lubrication systems, are used in the industry to provide air and a relatively small amount of seal gas at a relatively high pressure. It is important to remove particulates and condensates prior to injecting gas into an externally pressurized gas bearing; air quality Class 3 as defined by ISO 8573-1 is recommended for use in externally-pressurized gas bearings. See generally, Almasi, Turbomachinery International November/December 2013 issue. Use of conventional sealing systems that combine labyrinth and face/dry-gas seal technologies facilitate low flows from the small gaps positioned between the technologies. The buffer/flush gas provided in the small gap flows to a process side through the labyrinth. Similarly, a seal gas is provided that flows to a process side. The seal gas may be vented or flared. Some separation gas vents through a bearing chamber with a pumped-oil input. Temperature fluctuations in the bearing chamber cause large changes in oil viscosity and oil leakage from turbo systems creating serious problems; drains and coolers are used to control oil temperature.